Modulator



Oct. 25, 1938. G. UssELMAN v 2,134,065

MODULATOR original Filed March 21, 1931 2 sheets-sheet 2 CARR/ER l f4 66 AWMF/1? /2 10 LD50 5a 64 l I I g 52 1m/Hm Il.

u Ann An vvvvvvqlvv CARR/ER 50a/eff Fly 5 INVENTOR G. L. USSELMAN ATTORNEY Patented Oct. 25, 1938 UNITED STATES 2,134,065 lvroDULA'roitl George L. Usselman, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Original application March 21, 1931, Serial No. 524,247. Divided and this application January 29,1936, Serial No. 61,259

3 claims.

This invention relates to modulators and especially to sideband modulators of the electron discharge device type. This application is a division of United States application Ser. No.

ilv 524,247, led March 21, 1931, Patent #2,074,448,

dated March 23, 1937.

In order to produce sideband energy from carrier energy and energy of a frequencyV other than the carrier energy while at the same time suppressing the carrier energy,it has been pro-` posed to apply carrier energy to the grids of a pair of triodes cophasally and the other energy, usually modulating energy, to the same grids in phase opposition. By virtue of the fact that the two sources of energy were coupled to the same electrodes, undesired interaction between them frequently took place.

It is an object of this invention to provide a carrier suppression modulator wherein such interaction is effectively prevented. Briefly,.to do so, according to my present invention, I use four element or` screen grid tubes, or in other words, tubes having more than three electrodes for electron discharge devices, to like pairs of grids of which I apply either the modulating or carrier energy in phase opposition and to the other grids I apply the carrier or modulating energy cophasally. In this manner the energy sources are kept separate and prevented from interacting upon one another.

While the carrier or energy of higher order of magnitude in frequency may be applied to either of the grids of the screen grid tubes, I prefer to apply it cophasally to Athe screen grids of my improved carrier suppression modulator.

Sometimes it is desirable that a small amount of carrier energy be transmitted in addition to the sideband energy. Accordingly, a further object of the present invention isto provide an arrangement of electron discharge devices wherein carrier energy is only partially suppressed. More specifically, and one wayv of doing so, according to the present invention, grids of screen grid tubes are polarized differently and carrier alternating energy supplied thereto. Other grids of the system are supplied with modulating energy. As a consequence, in the output circuit of the tube arrangement, sideband energy and a certain amount of carrier energyv will appear.

Other general objects of my present invention are to provide transmitting and receiving systems utilizing my improved sideband or carrier suppression modulator.

While I have sought to define my invention in its broadest aspects in the appended claims, it may best be understood, however, both asv toV its structural organization and mode of operation by referring to the accompanying drawings, wherein: 5

Fig. 1 is a wiring diagram of a transmitting system having a sideband modulator therein comprising a pair of screen grid tubes to which carrier energy is applied to the screen grids cophasally and modulating energy to the usual 1 grids or grids adjacent the cathodes in phase opposition;

Fig. 2 is a schematic diagram of a receiving system using my improved carrier suppression modulator; u

Fig. 3 illustrates another form of my sideband modulator. wherein relatively low frequency energy is applied to the screen grids or grids adjacent the anodes of a pair of electron discharge devices and wherein relatively high frequency 2 energy is applied to the usual grids or grids adjacent the cathodes; and

Figs. 4 and 5 illustrate carrier suppression systems, according to the present invention, wherein the carrier is not totally but only par- 25 tially suppressed.

Referring to Fig. 1 of the accompanying drawings, relatively low frequency modulating energy, which may be considered energy of one order of magnitude in frequency, from a suitable amplifier 2 connected with source l is applied in phase opposition through the medium of transformer 4 to the usual grids 6 adjacent the cathodes 8 of electron discharge devices l0, of the screen grid type. To the screen grids I2 of thev grids adja- 35 cent to the anodes I4 of tubes I0, there is applied cophasally through conductors I6, I8 from a suity able source 20, carrier potentials or energy which may be considered energy of a diierent order of magnitude in frequency relative to energy from source 2.

By virtue of vthe application to the grids of electron discharge devices lll of energy of different frequencies,.there will appear in the out- 45 put circuit 22 coupled to the devices, energy of frequencies equal to the sum and diiTerence of the frequencies from sources 2 and 20. Energy of carrier frequency will not appear in the output circuit 22 for the reason that the carrier 50 energy is applied cophasally to the grids I2 and the carrier components appearing in the output circuit 22 effectively self cancel one another by virtue of the pushpull arrangement of tubes IB.

For successful operation,l the power supply 55 source for biasing the grids and especially the screen grids, should be very constant for otherwise a large regulation in biasing voltages on the grids would cause modulation of the carrier at frequencies corresponding to the regulation. For the same reason the regulation of the high frequency generator which supplies the carrier voltage-to the screen grids, should be constant to prevent extraneous modulation.

Inasmuch as the carrier and modulating energies are applied to different electrodes, they, are, of course, eifectually separated and cannot interact upon one another for the inter-electrode capacity coupling the two sources together is so small that the two sources can be considered for all practical purposes electrically separated.

Output energy from output circuit 22 may be fed, if desired, to a filter 24 and one sideband allowed to pass into an additional power amplifier or frequency multiplier or both included in 26 if found necessary. The amplified energy from amplifier 26 may then be radiated or electromagnetically propagated by the action of antenna 28.

If desired, the sideband modulator of Fig. 1 may be replaced by the scheme shown in Fig. 3 wherein carrier energy from source 20 is fed cophasally to the usual grids or grids adjacent the cathodes of tube I6; whereas the modulating energy is fed in phase opposition tothe screen grid of electron discharge devices I9. The output circuit 36 may be given a characteristic sufficiently broad to pass both sidebands generated or preferably, it is proportional so as to pass either the upper or lower sidebands produced as found desirable.

The output ,of pushpull connected screen grid tubes l may be taken from the output circuit 30 and fed to any suitable filter such as 24 of Fig. l, and then may, if found desirable, be impressed on a frequency multiplier and amplifier such as 26 of Fig. 1, and then may be transmitted by lmeans of a radiating antenna, such as 28 of Fig. 1.

It should be clearly understood, that a similar arrangement may be used wherein the voltage on the grids adjacent the cathodes is Varied in accordance with signal potentials by an arrangement similar to that shown in Fig. 3. lIn that event, the cathode and anode connections to the source 3 would be reversed so that a suitable biasing potential is applied to the usual grids. To the screen grids of such an arrangement high frequency energy would be applied cophasally as shown in Fig. 1.

My present invention is not, of course, limited to transmitting systems but may be used with equal advantages in a receiving system of the heterodyne type such as shown, for example, in Fig. 2. Electromagnetically propagated signal modulated energy collected upon antenna 32 may be amplified as desired by a radio frequency amplifier 34 and then fed in phase opposition to the grids adjacent the cathodes of electron discharge devices 36. Locally generated energy for producing intermediate frequency energy from a local oscillating source 38 is applied, as shown, to the screen grids of tubes 36, cophasally. The output circuit 40 of electron discharge devices 36 may be tuned or have suitable filters associated therewith to pass either the upper or lower sidebands into the intermediate frequency amplifier 42. I

Energy from intermediate frequency amplier 42 is then fed into a second detector or demodu- `lator 44 amplified, if desired, by a suitable low frequency amplifier 46 and translated by a suitable device such as telephones 48. It is to be clearly understood, of course, that in Fig. 2, for example, the incoming frequency energy may be fed to the screen grids of the tubes 36 either cophasally or in phase opposition in which cases the'locally generated energy would be applied to the usual grids of the tubes in phase opposition or cophasally respectively.

Should it be desired that a portion of the carrier energy appear in the output circuit of a modulator, arrangements such as shown in Figs. 4 and 5 may be used to good advantage.

In Fig. 4, signal modulating energy is applied to the grids 6, as shown, which are those adjacent the cathodes of devices I0. The screen grids I2 of tubes Ill are connected in parallel for high frequency currents by condenser 50 and are biased or polarized different amounts by independent taps 52, 54 leading to potentiometer 56 suitably supplied with potential as indicated. To prevent the flow of high frequency currents from source 20 in potentiometer 56, chokes 58 are inserted in series with the tapping connections 52, 54. As indicated above, the values of 56 and 58 are such that the high frequency energy from 20 is applied substantially in phase to the screen grids 20.

Consequently, carrier energy from source 20 will beV fed cophasally to the screen grids l2 by condenser 60, but, as the screen grids'l2A or grids adjacent the anodes of tubes I0 are polarized differently, a certain amount of carrier energy will always appear in the output circuit 62 of screen grids l0. The carrier energy and the sideband energy may then be amplified by suitable amplifier 64 and radiated by means of a suitable antenna 66.

Of course, by including in amplifier 64, suitable iilters, the carrier energy and one or the other sidebands may be transmitted as desired rather than transmitting both sidebands and the carrier.

The arrangement shown in Fig. differs from that shown inFig. 4 in that modulating energy is applied to the screen grids I2 or the grids adjacent the anodes of tubes I0 whereas carrier energy from source 20 is applied cophasally through the action of high frequency paralleling condenser 50 and reactance 12 to the grids 6 adjacent the cathodes of tubes l0.

In order to pass a certain amount of the carrier energy, a source of potential, here shown in the form of a battery 68, is inserted in series with the grids 6 and between the polarizing lead 'l0 for both grids. Source 68, therefore, will render the upper grid 6 different in static potential from that of `the lower grid 6 of the tubes I0. High frequency energy may be prevented from owing in the battery 68 and lead 'l0 by suitable choke coils 12. As an additional safeguard, lead may be grounded for radio frequency currents by condenser 14.

It is obvious that various minor changes will readily suggest themselves to Ithose skilled in the art. Consequently, my invention is not to be limited to themodications described, but solely by the scope of the claims which I have appended hereto. What is claimed is:

1. In a transmitting system, a pair of electron discharge devices each having a cathode, an anode, a grid adjacent the cathode and a grid adjacent-the anode, a common output circuit coupled to the anodes of said devices, a source of modulating energy, a balanced push-pull circuit coupling said source in phase opposition to the grids of said devices adjacent said cathodes, a source of relatively high frequency energy coupled cophasally Ato the grids adjacent said anodes through means separate from said rst named means, resistive means for applying different direct current potentials to the grids adjacent said anodes, means for amplifying the resultant energy in said output circuit, and means for transmitting the amplified energy.

2. In a system for transferring intelligence from one geographically situated point to ariother by propa-gated electro-magnetic wave energy derived from the ow of high frequency undulatory electrical currents operated upon in accordance with the intelligence to be transmitted, the combination of a pair of electron discharge devices each having a cathode, an anode, a grid adjacent the cathode and a grid adjacent the anode, resistive means for subjecting the gridsadjacent the anodes of said devices to uni-directional potentials of different values, means for subjecting the same grids to undulatory carrier potentials cophasally, and balanced circuit means for subjecting the grids of said devices adjacent said cathodes to potentials of another order of frequency and in phase opposition.

3. In a signalling system the combination of a pair of electron-discharge devices, each having a cathode, an anode, a grid-like electrode adjacent the cathode, and a grid-like electrode adjacent the anode, circuits including a source of direct current potential connected with the grid-like electrodes adjacent said anodes for applying thereto direct current potentials of different value, a reactance in each of said circuits, a source of wave energy, a circuit connecting said source of wave energy in parallel with the gridlike electrode in each of said devices adjacent the anode for applying to said electrodes wave energy in phase, asource of modulating potentials, and transformer means interposed between said source of modulating potentials and the grid-like electrode in each of said devices adjacent the cathode to apply thereto modulating potentials in phase opposition.

GEORGE L. USSELMAN. 

